US3479853A

US3479853A - Hot rolling of light gauge strip

Info

Publication number: US3479853A
Application number: US664896A
Authority: US
Inventors: George L Berry
Original assignee: Jones and Laughlin Steel Corp
Current assignee: Jones and Laughlin Steel Corp
Priority date: 1967-08-29
Filing date: 1967-08-29
Publication date: 1969-11-25
Anticipated expiration: 1986-11-25
Also published as: DE1777024A1; FR1579762A; GB1191355A

Description

New. 25, @1969 BERRY 3,479,853

HOT ROLLING OF LIGHT GAUGE STRIP 2 Sheets-Sheet 1 Filed Aug. 29, 1967 GEORGE L. BERRY BY his ATTORNEY NW0 W69 5. L. BERRY HOT ROLLING OF LIGHT GAUGE STRIP 2 Sheets-Sheet 2 Filed Aug. 29, 1967 INVENTOR.

GEORGE L. BERRY his ATTORNEY nited States Patent 3,479,853 HOT ROLLING OF LIGHT GAUGE STRIP George L. Berry, Pittsburgh, Pa, assignor to Jones &

Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 29, 1967, Ser. No. 664,896 Int. Cl. B21b 27/10 US. Cl. 72128 8 Claims ABSTRACT OF THE DISCLOSURE Light gauge strip is hot rolled in a conventional tandem mill, coiled in a coiler placed close to the delivery stand of the mill, and cooled by high pressure sprays, the upper sprays being positioned immediately above the runout table.

This invention has to do with the production of light gauge hot rolled strip, particularly steel strip, on continuous mills. Conventional continuous hot strip mills are constructed for the primary purpose of accepting slabs and rolling them into coils of hot band, which has a thickness from about .100 up to about .375". This hot band is then further reduced in thickness by cold rolling. These mills are also capable of producing hot rolled strip, which is lighter in gauge than hot band and is sold without any subsequent cold rolling. Prior to my invention to be described hereinafter hot rolled strip of less than about 14 gauge was very difficult to produce on continuous mills, and the production of such strip as thin as 18 gauge was considered to be quite impractical.

Hot band is conventionally delivered from the hot strip mill at speeds of about 900 to 2500 feet per minute onto a long run-out table comprising a succession of rolls and provided at the far end with coiling means. Hot band is conventionally delivered at temperatures on the order of 1600 to 1700 F. and as it passes down the run-out table it is subjected to sprays or streams of water or other cooling liquid to cool it to coiling temperatures desired for metallurgical reasons. Those temperatures are usually not less than about 1000 F. The apparatus required to deliver cooling water sufiicient for this purpose may be several hundred feet in length. Run'out tables in lengths of 450 to 500 feet are not uncommon.

The strip on the run-out table is usually cooled by application of cooling water both to its top and bottom surfaces. The cooling of the bottom surface is accomplished by spray headers positioned a few inches below the strip between the rools of the run-out table. The application of cooling water in sprays or streams to the top of the strip is also accomplished by liquid delivery means positioned above the strip, but these must be spaced far enough above the strip so that they are not damaged when the stri cobbles on the min-out table.

Cobbling occurs when a succeeding portion of the strip traveling along the run-out table overruns a foregoing portion. Cobbling may happen at any stage in the rolling of a coil, but as the result of circumstances which are peculiar to those stages. At the beginning of rolling of a coil, cobbling is caused by aerodynamic forces which tend to lift the head end of the coil off the run-out table. This effect is aggravated by camber in the strip and is most pronounced with light strip gauges and higher coiling speeds. During the rollings of the body of the coil, the strip is in tension between the finishing stand of th mill and the coiler, and cobbling is occasioned usually by some form of speed mismatching. At the end of the coil, cobbling may occur if the tension in the stri has not been sufficiently reduced in advance of the exit from the finishing stand of the trailing end. The end suddenly "ice freed snaps up, overtakes the strip ahead of it on the run-out table, and piles up on it. To avoid or minimize damage to the upper cooling liquid delivery means by such cobbles, it is conventional to locate those means five or six feet or so above the run-out table surface.

Those skilled in the art of cooling hot strip know that the factor limiting the rate of strip cooling is the layer or blanket of steam which forms on the surface of th strip and impedes heat transfer therefrom to the cooling water. This heat transfer is not greatly improved by increasing the pressure at which the water is delivered when this delivery is effected several feet above the strip surface. Increasing the spray pressure increases the initial velocity of the water droplets but also decreases the size of those droplets. Small droplets have a high ratio of surface to volume and rapidily lose their momentum as they travel toward the strip through friction of the air. Also the smaller droplets are more easily diverted by the esca ing steam. In recent years efforts have been directed toward improving heat transfer by reducing the delivery pressure of the water and causing it to fall onto the strip in more or less coherent non-turbulent streams, as is described in Adcock Patent No. 3,025,865 and Maruszewski, et al. Patent No. 3,294,107.

Hot rolled strip of light gauge cools in the tooling much faster than strip of hot band gauge and must therefore be delivered from the finishing stand of the hot strip mill at high speeds if it is to be rolled at the temperatures desired for metallurgical reasons. This delivery speed is on the order of 3500 feet per minute for strip of 19 gauge or less. When hot rolled strip of these gauges is delivered at such speeds onto a conventional run-out table, strip instability develops because of the aerodynamic effects which appear under these conditions. The reaction between the rapidly moving strip and the surrounding air results in lifting forces which cause the strip to kite, or tend to rise from the table. This tendency is most prevalent during the threading operation, when the strip is not in tension. However, because of the risk of tearing the strip, the tension cannot be increased during rolling sutficiently to overcome this action. The strip therefore flutters, or rises and falls in an irregular fashion, particularly at the edges, and side slips, or moves transversely of the table. Because of this flutter or oscillation, the strip is difficult to coil, tending to telescope with consequent damage to its edges and surface. Further, the unbalanced forces acting on the strip during such cooling and coiling adversely affect its flatness, and may tear it. Even when the difiiculties above mentioned are overcome, it is found that light gauge strip transported over a run-out table of adequate length for hot band cools so fast that it must be coiled at temperatures lower than those required for a number of metallurgical purposes.

It is an object of my invention, therefore, to provide method and apparatus for cooling and coiling continuously hot rolled strip of gauges lighter than about 18 gauge. It is another object to provide such apparatus which is compatible with apparatus conventionally used for cooling and coiling heavier gauge hot rolled strip. It is another object to provide a novel cooling method and apparatus adapted for light gauge strip. Other objects of my invention will appear in the description thereof which follows.

I have found that strip of 19 gauge to as thin as 24 gauge (.047" to .025") hot rolled at delivery speeds required for the desired finishing temperatures can be coiled satisfactorily in a coiler positioned at a distance from the mill less than that in which detrimental strip flutter develops. I have further found that trailing end cobbling of such strip will not develop in the distance between the mill and my coiler so positioned. I therefore cool the strip between mill and coiler to metallurgically acceptable temperatures with high pressure sprays of water or other cooling liquid placed close to the strip.

I have found that light gauge strip rolled at high speed can be coiled satisfactorily if the distance between the mill and the coiler is relatively short. By relatively short I mean many times less than the distance between the mill and the coiler in conventional continuous hot strip mill installations which, as I have mentioned, may be 400 to 500 feet. I have not determined the maximum spacing between mill and coiler in which the strip will not develop flutter detrimental to coiling, as this distance is influenced by the width of the strip. I do not believe there is any minimum distance as far as strip flutter is concerned, but the coiler must, of course, be spaced from the mill by the strip cooling apparatus. The amount of space required for cooling is not dependent on the Width of the strip, as the cooling apparatus can take the form of cross-headers spaced along the run-out table, each header being provided with a plurality of sprays or nozzles. Wide strip does not require any more cross-headers than narrow strip, but merely lOnger cross-headers with more nozzles.

Conventionally, the cooling apparatus for the upper surface of the strip has been spaced above the strip a distance greater than that ordinarily reached by strip cobbles on the run-out table. This is a necessary precaution in a mill rolling hot band as the weight of the hot band is considerable and its impact against cooling apparatus will damage it. I have found, however, that if the coiler is close enough to the mill and light gauge strip is delivered at high speed, its trailing end reaches the coiler before it can cobble.

I have also found that when the coiler is placed close to the mill, the absence of strip flutter makes feasible the use of strip guides so that coils of hot rolled strip comparable to coils of cold rolled strip can be produced.

I therefore cool the strip to coiling temperature by high pressure sprays positioned close to the strip surface intermediate the mill and the coiler. Here again the terms high and close must be construed in the context of the prior art. As I have mentioned the tendency in modern strip mills is to go to so-called laminar flow cooling systems which operate at atmospheric pressure or slightly above. The sprays which cool the underside of the strip in conventional installations are close to the strip, as they must be placed between the rolls of the run-out table and are protected by its rolls from being damaged by cobbles. They must, however, be operated at pressures below those which lift the strip off the run-out table. I utilize lower sprays conventionally positioned below the strip, and upper sprays positioned above the strip a distance of the same order as that between the strip and the lower sprays. The upper sprays therefore counterbalance the lower, and I supply cooling fluid to them at pressures many times atmospheric pressure, and several times the pressures of lower sprays in conventional installations. Preferably I supply cooling fluid at pressures of about 250 lbs. per square inch.

I protect my upper sprays from possible damage by strip tearing or breaking by means to be described.

An embodiment of the apparatus of my invention presently preferred by me is illustrated in the attached drawings, to which reference is now made.

FIGURE 1 is as schematic elevation of the apparatus of my invention.

FIGURE 2 is a vertical cross-section through the apparatus of my invention taken on the plane 2-2 of FIG- URE 1.

FIGURE 3 is a plane of the apparatus of FIGURE 2.

The strip which passes through my apparatus is delivered from the delivery stand 1 of a conventional continuous hot strip mill onto a run-out table 2. Table 2 comprises a succession of transverse parallel driven rolls 33. At the other end of run-out table 2 is positioned a pair of driven pinch rolls comprising upper roll 4 and lower roll 5. Above table 2 is positioned a longitudinal header pipe 6 parallel to the long axis of run-out table 2 and located at one side thereof. From header pipe 6 project horizontal transverse header pipes 77 over run-out table 2. Below table 2 is positioned a longitudinal header pipe 8 parallel to the long axis of run-out table 2 and located at one side thereof. From header pipe 8 project horizontal transverse header pipes 99 beneath runout table 2, each pipe 9 being positioned between adjoining rolls 33. Each transverse header pipe 7 and each transverse header pipe 9 is provided with a plurality of spray nozzles 1010, equally spaced from each other along the pipe and directed toward the strip.

On the other side of pinch rolls 4 and 5 is positioned a second run-out table 12 which is a continuation of runout table 2 and which likewise comprises a succession of transverse parallel driven rolls 33. Beneath run-out table 12 and immediately following pinch rolls 4 and 5 is positioned a strip down-coiler 13, suitable for light gauge strip, including a mandrel 14, about which the strip is coiled. Coiler 13 is provided with a drive motor, which is not shown. Immediately adjacent the delivery side of the pinch rolls 4 and 5 is located a moveable gate 15 which can be caused to pivot around a horizontal shaft 16 in its end remote from pinch rolls 4 and 5. When gate 15 is in its raised position, as is shown in FIGURE 1, it diverts strip passing through pinch rolls 4 and 5 downwardly toward guide 17, which is inclined downwardly and away from run-out table 12 toward mandrel 14 of coiler 13. When gate 15 is in its lowered position it permits strip passing through pinch rolls 4 and 5 to pass over run-out table 12.

At the far end of run-out table 12 is positioned a second pair of pinch rolls comprising upper pinch roll 18 and lower pinch roll 19. At the exit side of pinch rolls 18 and 19 is a second gate 20. Strip diverted downwardly by gate 20 is guided by guide 22, which is identical with the guide 17 previously mentioned, onto a mandrel 23 of a second coiler 24. Coiler 24 is also a down-coiler.

Intermediate coilers

13 and 24 and above run-out table 12 is positioned a longitudinal header pipe 26 parallel to the long axis of table 12 and at one side of that table. Froin header pipe 26 project horizontal transverse header pipes 2727 which are similar to transverse header pipes 77 previously mentioned. The transverse header pipes 2727 are elevated about 6 feet above the upper surface of run-out'table 12. Below table 12 is positioned a longitudinal header pipe 28 parallel to the long axis of the table and at one side of the table. From header pipe 28 project horizontal header pipes 29-29 beneath run-out table 12, each transverse header pipe 29 being spaced between adjoining rolls 33. Each upper header pipe 27 is provided with a plurality of downwardly directed liquid delivery pipes 3030, equally spaced from each along the pipe. Each header pipe 29 is likewise provided with a plurality of upwardly directed spray nozzles 3131, equally spaced from each other along the pipe.

The transverse header pipes 77 previously mentioned are arranged so that they can be swung upwardly about the axis of longitudinal header pipe 6 entirely clear of run-out table 2. The structure which accomplishes this purpose is illustrated more particularly in FIGURES 2 and 3. Longitudinal header pipe 6 is supported at each end in bearings 35-35, which bearings in turn are mounted on pedestals 36-36. The water is conducted into one end of header pipe 6 by a supply pipe 37 which connects to header 36 through a sliding joint so as to allow a pivotal movement of the header. Attached to header pipe 6 is a crank arm 39 positioned so that it normally extends above header pipe 6. The closed end of hydraulic cylinder 40 is pivotally fastened to a pedestal 41 positioned on the opposite side of longitudinal header pipe 6 from run-out table 2. The piston rod 42 of cylinder 40 is pivotally attached at its outer end to crank 39. Hydraulic accumulator 43 is attached to pedestal 41 and provides a reservoir of fluid under pressure for operating cylinder 40. The supply lines and control valves for this apparatus are not shown as they are conventional. Counterweights 44-44 are attached to header pipe 6 so as to counterbalance part of the weight of the assembly of transverse header pipes 7-7.

The outer ends of transverse header pipes 7-7 are braced by a longitudinally extending member 45. Above header pipes 7-7 and attached to them is positioned a cover or shield 46 to confine the splashing from the sprays 10-10. Intermediate the ends of member 45 is attached a downwardly and outwardly extending member 47 which, when the transverse header pipes 7-7 are parallel to run-out table 2, abuts a pedestal 48. Pedestal 48 carries a locking pin 49 and an actuator 50 therefor, which pin engages an opening in the end of member 45 so as to lock the transverse header assembly in its operating position when it is in use.

In order to protect spray nozzles 10-10 and transverse header pipes 7-7 from possible injury by cobbles resulting from strip breaks and likewise to prevent a strip end from projecting itself between transverse header pipes 7-7, there are provided longitudinally extending rail members 52-52 which are fastened to the underside of header pipes 7-7 between nozzles 10-10 and extend the full length of the space between the first and the last transverse header pipe 7. These rail members 52 extend below the openings of spray nozzles 10-10 and so form a grid which does not interfere with the delivery of cooling liquid from sprays 10-10 but protects the spray and their associated piping from damage.

Transverse header pipes 7-7 are provided with individual valves 53-53 so that the number of headers to be used may be adjusted at will. Individual valves 54-54 are also provided for lower transverse header pipes 9-9 for the same reason.

The operation of my apparatus will be explained in connection with the attached figures. When light gauge strip is to be rolled, its leading end is threaded through pinch rolls 4 and 5, and transverse header pipes 7-7 are positioned above the run-out table 2 as is shown in FIGURE 2. Projecting member 45 is locked to pedestal 58 by locking pin 49 so that the spray nozzles 10-10 of transverse header pipes 7-7 are fixed in position directly above run-out table 2. Pinch rolls 4 and 5 are then separated, and gate is moved to the position shown in FIGURE 1 so that the strip introduced between pinch rolls 4 and 5 is deflected by guide 17 toward the mandrel 14 of coiler 13. After the leading end of the strip is secured to mandrel 14, the drive motor for coiler 13 is started up and is accelerated, as are the drive motors for the stands of the mill, until the desired rolling speed is achieved. The speed of the drive motor for coiler 13 is adjusted so as to maintain tension in the strip between coiler 13 and exit stand 1 of the mill. Water or other cooling fluid is sprayed onto the strip through nozzles 10-10 in upper headers 7-7 and lower headers 9-9.

The cooling fluid discharged from the upper and lower spray nozzles 10-10 positioned close to the strip surface cools the strip rapidly from its delivery temperature to the desired coiling temperature. As the length of strip between exit stand 1 and coiler 13 is relatively short, the strip does not become unstable at the high rolling speeds required, and so coils smoothly without telescoping. Before the trailing end of the strip leaves exit stand 1 both the mill motors and the drive motor for coiler 13 are adjusted so as to reduce the tension in the strip immediately prior to the exit of its trailing end from the mill.

Should the trailing end of the strip leave exit stand 1 under relatively high tension, it will, of course, snap up against the upper sprays. However, the trailing end will not damage the transverse headers 7-7 or the nozzles 10-10 afiixed thereto, nor will it cobble, because its impact will be taken by longitudinal rails 52-52 which project below nozzles 10-10.

Should the strip break intermediate exit stand 1 and coiler 14, the trailing end of the forward portion will, of course, go into the coiler 13. The leading end of the remaining portion will be pushed over run-out table 2 under zero tension. In these circumstances, the speed of the mill is immediately reduced and cobbling is avoided by opening pinch rolls 4 and 5 and lowering gate 15 so that the strip is pushed between pinch rolls 4 and 5 onto run-out table 12 which extends beyond them. After the strip end has passed through pinch rolls 4 and 5, they are closed upon it and operated at a speed such that tension is maintained between them and the exit stand 1 of the mill.

When hot band is to be rolled by the mill, the upper sprays intermediate the exit stand 1 and coiler 14 are swung up around the axis of longitudinal header 6 by admitting fluid under pressure to the piston rod end of cylinder 40. Pinch rolls 4 and 5 are opened and gate 15 is lowered. The hot band delivered by exit stand 1 is then caused to move over run-out table 2 onto run-out table 12 and into coiler 24, and is cooled by the cooling system positioned between coiler 13 and coiler 24.

In one installation of the apparatus of my invention with which I am familiar, the distance from the centerline of exit stand 1 of the mill to the centerline of coiler mandrel 14 is 37 feet. The spacing between the upper surface of lower cross-headers 9-9 and the surface of run-out table 2 is about 5 inches and that between the lower surface of upper cross-headers 7-7 and the surface of run-out table 2 is about 11 inches. The lower sprays supplied by lower cross-headers 9-9 discharge cooling water at the rate of 2500 gallons per minute at a pressure of 250 pounds per square inch. The upper sprays supplied by upper cross-headers 7-7 are identical with the lower sprays.

I claim:

1. Apparatus for the cooling and coiling of hot rolled light gauge strip delivered directly from a hot strip mill over a run-out table into a strip coiler comprising a bank of high pressure cooling liquid sprays positioned above the run-out table at a distance therefrom sufiicient to cause droplets of cooling liquid delivered by the spray nozzles to penetrate the layer of steam formed by evaporation of cooling liquid on the strip and impinge thereon in heat transfer relation therewith, that distance being many times less than the height reached by strip cobbles on the run-out table in the absence of sprays and means adapted to protect the spray nozzles from contact with strip cobbles positioned between the spray nozzles and extending below them longitudinally over the length of the bank of high pressure sprays and attached thereto, the spray nozzles being distributed to deliver cooling liquid across the width of the run-out table and along a portion of its length sufficient to cool the strip from delivery temperature to coiling temperature, and the strip coiler being positioned immediately following the bank of high pressure sprays,

2. Apparatus of claim 1 in which the means adapted to protect the spray nozzles from contact with strip cobbles comprise a plurality of rails.

3. Apparatus for the cooling and coiling of hot rolled light gauge strip delivered directly from a hot strip mill over a run-out table into a strip coiler comprising a bank of high pressure cooling liquid sprays positioned above the run-out table at a distance therefrom sufficient to cause droplets of cooling liquid delivered by the spray nozzles to penetrate the layer of steam formed by evaporation of cooling liquid on the strip and impinge thereon in heat transfer relation therewith, that distance being many times less than the height reached by strip cobbles on the run-out table in the absence of the sprays, the spray nozzles being distributed to deliver cooling liquid across the width of the run-out table and along a portion of its length suflicient to cool the strip from delivery temperature to coiling temperature, the strip coiler being positioned immediately following the bank of high pressure sprays, the bank of high pressure sprays being mounted for pivotal movement about an axis parallel to a longitudinal edge of the run-out table and positioned outside that table and above it, and means attached to its edge opposite that axis cooperating with means attached to the run-out table to releasably lock the spray bank to the run-out table.

4. Apparatus for the cooling and coiling of hot rolled light gauge strip delivered directly from a hot strip mill over a run-out table into a strip coiler, the gauge and speed of delivery of the strip being sufiicient to develop strip flutter detrimental to coiling through aerodynamic reaction between the strip and the atmosphere surrounding the run-out table, comprising a bank of high pressure cooling liquid sprays positioned above the run-out table at a distance therefrom sufiicient to cause droplets of cooling liquid delivery by the spray nozzles to penetrate the layer of steam formed by evaporation of cooling liquid on the strip and impinge thereon in heat transfer relation therewith, that distance being many times less than the height reached by strip cobbles on the run-out table in the absence of the sprays, the spray nozzles being distributed to deliver cooling liquid across the width of the run-out table and along a portion of its length sufficient to cool the strip from delivery temperature to coiling temperature, the strip coiler being positioned immediately following the bank of high pressure sprays a distance not more than that in which strip flutter detrimental to coiling develops.

5. Apparatus of claim 4 adapted for the coiling and cooling of strip of 19 to about 24 gauge, delivered at a speed of about 2400 feet per minute to about 3500 feet per minute in which the distance between the hot strip mill and the strip coiler is not more than about 40 feet.

6. The process of cooling and coiling hot rolled strip delivered from a continuous hot strip mill onto a run-out table, the gauge and speed of delivery of the strip being sufficient to develop strip flutter detrimental to coiling through aerodynamic reaction between the strip and the atmosphere surrounding the run-out table, comprising spraying cooling fluid against the lower surface of the strip from a plurality of lower spray nozzles positioned beneath the strip and spraying cooling fluid against the upper surface of the strip from a plurality of upper spray nozzles positioned above the strip a distance of the same order as that between the lower sprays and the strip, the sprays being operated at a pressure many times greater than atmospheric pressure so as to cause the droplets of sprayed cooling fluid to penetrate the layer of steam on the strip formed by evaporation of cooling fluid thereon and to impinge on the strip in heat transfer relation therewith, the spray nozzles being arranged and adjusted to cooling and strip from delivery temperature to coiling temperature in a strip travel distance less than that in which strip flutter detrimental to coiling develops, and then immediately coiling the strip.

7. The process of claim 6 in which the lower sprays are adjusted to exert force on the strip greater than that sufiicient to lift the strip from the run-out table in the absence of the upper sprays and the upper sprays are adjusted to provide a net downward force on the strip.

8. The process of claim 6 in which the distance from the sprays to the strip is not more than about one foot and the sprays are operated at a pressure of about 250 pounds per square inch.

References Cited UNITED STATES PATENTS 1,108,144 8/1914 Daniels 72-428 1,684,867 9/1928 Johnson 72l28 2,211,981 8/1940 McBain et al. 72-201 2,696,823 12/ 1954 Scott. 3,300,198 1/1967 Clumpner et al.

MILTON S. MEHR, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,479,853 November 25, 1969 George L. Berry It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 51, "rools" should read rolls line 66, "rollings" should read rolling Column 2, line 25, "rooling" should read rolling Column 3, line 69, "plane" should read plan Column 8, line 15, "cooling and" should read cool the Signed and sealed this 20th day of October 1970.

(SEAL) Attest:

Attesting Officer Commissioner of Patents